function [E, nu] = cal_Ev(lambda, mu)
%function [E, nu] = cal_Ev(lambda, mu)
% a tool function used to calculate E and nu according to lambda and nu
    x = fsolve(@(x) fun(x, lambda, mu), [-1000, 1000]);
    E = x(1);
    nu = x(2);
end

function F = fun(x, lambda, mu)
    E = x(1); nu = x(2);
    F = [E*nu - lambda*(1+nu)*(1-2*nu); ...
           E - 2*mu*(1+nu)];
end